The preparation of cyclic ureas is known in the art. Cyclic ureas of 5, 6 and 7 membered atoms are not difficult to prepare. They are often synthesized by the reaction of diamines with phosgene, urea or carbon dioxide. Methods for the preparation of higher molecular weight cyclic products are complicated by the side reaction of linear polycondensations. (See G.A. Settepani et al, J. Heterocyclic Chem. 10,639 (1973); J. Michus, J. Org. Chem. 25, 2246 (1960); L. Birkofer et al., Chem. Ber. 93, 2810 (1960).
Large ring cyclic ureas can also be prepared by careful reaction of diisocyanates with water utilizing a high dilution technique. For example, utilizing 900 ml of acetone and 900 ml of water as reaction media, 3.2 g of octamethylene diisocyanate in 70 ml of acetone was added over a 17 hour period in a special Hunsdiecker apparatus. The yield was 18%. ##STR1## The yields increased to 49% for a 13 membered ring, 41% for a 15 membered ring and 36% for a 17 membered ring. See S. Ozaki et al., J. Am. Chem. Soc. 79, 4358 (1957)
In Synthesis, 1982, 464, A.V. Bogatsky et al. disclose that macrocyclic thioureas can be obtained by the reaction of carbon disulfide. Bogatsky et al. disclose that cyclic thioureas with alkyl halides in the presence of aqueous sodium hydroxide and catalytic amounts of benzyltriethylammonium chloride produce the corresponding N,N'-dialkylureas in good yields. ##STR2## Further, they suggest cyclic N,N'-dialkylureas of 5 to 22 carbon atoms could be prepared using this method. The macrocyclic polyoxyethylene ureas are described by this group as a new type of crown ether. Large cyclic rings allow the carbonyl groups to orient themselves into the cavity which permits coordination of a metal ion with both the ether and the carbonyl oxygen atoms. Ligands such as those below would interact with lithium, sodium and potassium ions (R=alkyl). ##STR3##
Later, N.G. Lukyanenko et al., reported in Synthesis, 1986, 928, that macrocyclic thioureas may be converted to macrocyclic ureas by another route which can be represented by the following: ##STR4##
As noted, in a number of the methods for preparing cyclic ureas found in the art, disadvantages include side reactions involving linear polycondensations and the need to first prepare a diisocyanate derivative of the diamine. Cyclization of the diisocyanate requires very high dilution techniques.
U.S. Pat. No. 3,763,106 is of interest for teaching a different result using similar reactants to those which are found useful in the instant invention.
It would represent a substantial advance in the art if cyclic ureas could be prepared from commercially available reactants such as diamines and urea under very controlled reaction conditions without the necessity for high dilution techniques.